Strength Enhancement of Clay Through Lime-Sand Stabilization at Various Remolding Water Contents

During the construction of subgrade, the remolding water content w of lime-sand-stabilized clay usually varies in a wide range, leading to inconsistent effectiveness in strength enhancement. Until now, this aspect has not been investigated. In this study, an unconfined compression test and microscopic observation were carried out on clay and stabilized clay (adding 4% lime by mass and 50% sand by volume). The results show the following: (1) remolding water content w had a strong effect on the soil fabrics of pure clay and lime-stabilized clay. An increase in the w from the dry to wet side of optimum reduced matric suction, which diminished the aggregation effect among fine-grained particles in both clay and lime-stabilized clay. Correspondingly, fine-grained aggregate progressively disintegrated, and dispersed fine-grained particles increased. As a result, the w increment at w ≤ w_cha made the dispersed fine-grained particles successively fill the large pores between aggregates, densifying the soil fabric. In contrast, at w > w_cha, the ongoing disintegration of aggregate resulted in progressive structural weakening. Herein, w_cha was defined as the characteristic water content at which the soil fabric transitioned from structural densification to weakening. (2) The UCS of both pure clay and lime-sand-stabilized clay followed a bell-shaped pattern as the w increased, with w_cha acting as the turning point. For pure clay soils, the UCS increased with increasing w up to w_cha because of structural densification, but decreased beyond w_cha due to structural weakening. In lime-sand-stabilized clay, where a sand grain skeleton developed, the compression of lime-stabilized clay induced by the movement of sand grains during shearing activated its contribution to the overall strength. The compressive capacity of the lime-stabilized clay varied in a bell-shaped manner with w, and this trend was mirrored in the UCS of lime-sand-stabilized clay. (3) At a low w, the fact that the clay aggregate exhibited sand-like mechanical behavior reduced the effectiveness of incorporating sand and lime for enhancing the UCS. As the w increased at w ≤ w_cha, the breakdown of aggregates enlarged the distinction between pure clay and sand, resulting in a more pronounced improvement in the UCS with the addition of sand and lime. At w > w_cha, the lubrication effect occurring at the contact between sand grains diminished the interlocking between the sand grains. Consequently, the effectiveness of the UCS enhancement decreased.